1. Field of the Invention
The present invention relates to a charging and discharging control device for extending a cycle life of a secondary battery.
2. Description of Related Art
In Japanese Unexamined Patent Publication (Kokai) No.63-55868, there is disclosed a conventional charging and discharging control device for the secondary battery, which controls the charging and discharging operations of the battery upon a previous establishment of predetermined reference values as a charge stop voltage and discharge stop voltage, respectively.
In this conventional device, however, there is a tendency that a deterioration rate of battery-capacity of the secondary battery increases gradually as a number of charging/discharging cycle thereof increases. For example, in case of employing the secondary battery (or batteries) as a battery for driving a motor of vehicle, there is raised a problem that a basic performance of vehicle, such as a traveling range of the vehicle per charging, is abruptly deteriorated as times pass.
Further, under condition that a plurality of secondary batteries are used as a builtup battery and that, at discharging, the discharging operation as the whole builtup battery is stopped by either one discharge-completion signal generated from one secondary battery or limited numbers of discharge-completion signals of specified secondary batteries, it is not possible to make use of energy contained in all of the secondary batteries efficiently due to difference in battery-capacity between respective secondary batteries.
Similarly, because of a difference between individual secondary batteries, there is a problem that the more the battery is deteriorated, the more it shortens the life span of the builtup battery.